1. Field of the Invention
The present invention relates generally to the field of environmental control devices and methods and, more specifically, to electrical arcing environmental devices for reducing emissions in an exhaust stream and, also, for generating ozone for other environmental purposes.
2. Description of the Related Art
Combustion engines of automobiles, trucks, aircraft, and other sources emit millions of tons of pollutants, such as, oxides of nitrogen, hydrocarbons, carbon monoxide, carbon dioxide, and air toxics, every year. Other significant contributors to air pollution include, for example, electrical power generators, coating processes, and solid waste incineration, among others. Due to expanding industrialization and increasing world-wide use of automobiles, the problems caused by air pollution are an ongoing and increasing concern.
Generated pollutants degrade public health and damage the environment. For example, carbon monoxide, a toxic by-product of incomplete combustion, is a major contributor to air pollution and effects public health. As another example, carbon dioxide, although non-toxic, directly contributes to the “greenhouse effect”. Moreover, hydrocarbons may cause eye irritation, nasal congestion and breathing difficulties. And, air toxics are carcinogenic.
In an effort to curb air pollution, many countries have promulgated air pollution emission standards that require pollution sources to be controlled by best available technology. Such known pollution control technology includes electrostatic precipitators, wherein a voltage difference is impressed between electrodes positioned in an exhaust stream. The voltage ionizes gas particles in the exhaust stream, which in turn causes particulate matter that is suspended in the gas to acquire a charge from being in contact with the ionized gas particles. The charged particles are then collected at oppositely charged diodes that must be routinely “cleaned” or “scrubbed”. A significant drawback of electrostatic precipitation is that only minute particulate matter can be precipitated out of the exhaust stream. Moreover, this process is ineffective at removing gaseous contaminants such as oxides of nitrogen, carbon dioxide, carbon monoxide, and air toxics.
Other conventional air pollution control devices include baghouses and cyclones which are used to control emissions of particulate matter. Baghouses remove particulate matter by placing a plurality of filter bags in an exhaust stream. The bags filter entrained particulate matter from the exhaust stream as it passes there-through. Cyclones remove particular matter by directing the air stream in a spiral motion whereby tangentially moving particles settle out of the air stream due to the laminar boundary layer formed along the interior surface of the cyclone. Both of these air pollution control devices are subject to spontaneous combustion and, thus, are not suitable for use in high temperature environments. Moreover, both control devices are ineffective at removing gaseous pollutants and require considerable maintenance.
Still other conventional air pollution control devices include burners, granular activated carbon and water curtains. These control devices are typically used for reducing hydrocarbons and volatile organic compound emissions in an exhaust stream. However, the configuration and operational requirements of these devices make them unacceptable for many applications. Fox example, burners require a high temperature flame, water curtains require a supply of water and activated carbon quickly clogs when subjected to particulate laden exhaust.
With regards to automobiles, catalytic converters having precious metals, such as a troy ounce of platinum, palladium or rhodium, are currently being used to reduce tailpipe emissions. These precious metals are expensive and have a limited world-wide supply. Thus, their availability is insufficient to meet world-wide requirements, particularly in developing countries.
Moreover, catalytic converters have a limited useful life, throughout which their efficiency diminishes. And, for some vehicle models, even a new catalytic converter is unable to meet vehicle emissions standards thereby requiring a plurality of catalytic converters to be placed in series in order to treat the exhaust. Once a catalytic converter is spent, the precious metals therein are not easily solvable and, therefore, are typically landfilled as a hazardous waste.
A relatively recent innovation for reducing pollutants in an exhaust stream is to apply a corona field to the exhaust. However, corona generating devices are very limited in the type of pollutants that they can remove from an exhaust. Accordingly, corona devices have no practical applicability for controlling emissions from most industrial sources or from vehicles.
An example of a corona discharge device is shown in U.S. Pat. No. 5,733,360 to Feldman, which discloses a method and device for chemically activating various constituents of a gas stream by use of a corona discharge. To create a corona field, Feldman uses fine, wire-like electrodes extending from one of a pair of discharge plates. The voltage is applied in such as manner and in such short duration as to suppress the formation of sparks across the gap between the electrodes. According to Feldman, the device seeks to reduce pollutants through the use of a spatially distributed corona discharge cloud.
Another example is U.S. Pat. No. 5,433,832 to Rich, which discloses a dielectric discharge device, also known as a “silent discharge” device, for reducing pollutants in an exhaust. The device applies voltage between electrodes to cause a cloud of electrons and ions to be formed between the electrodes. To ensure that the electron/ion cloud is created, one of the electrodes is encased in a dielectric and the voltage is applied in such as manner as to prevent arcing between the electrodes.
Henis, U.S. Pat. No. 3,983,021, is also a corona discharge reactor known as a “silent discharge” reactor. The reactor removes nitrogen oxides from gases by solids contact and electric discharge. The electric discharge utilizes a dielectric and/or a packing material between electrodes to inhibit sparking or arcing between electrodes in order to generate a corona field.
An excited species generator is disclosed by Nunez, U.S. Pat. No. 5,236,672, which provides excited species to oxidize volatile organic compounds and other pollutants within a fluid stream. Electrodes of the excited species generator are fabricated from tungsten, or tungsten projections are applied to the electrodes, in order to allow for voltage to be provided across the electrodes without arcing or sparking.
An emission control device for reducing pollutants in an exhaust gas is shown by Masters, U.S. Pat. No. 5,410,871. The device includes a treatment chamber having a first metal screen, a second metal screen, and an electrode disposed a distance from the first screen. Voltage is supplied so that sparks are generated between the electrode and a concentrated location on the first screen. Consequently, the sparks traverse only a minute portion of the gas, leaving the vast majority of the exhaust gas unaffected.
In another patent to Masters, U.S. Pat. No. 5,419,123, an emission control device is described that includes a treatment chamber having a first metal screen, a second metal screen and a perforated chemical substrate disposed between the first and second screens. An electrode, disposed a distance from the first screen, is supplied a voltage so that sparks are generated between the electrode and a concentrated location on the first screen. Consequently, the sparks traverse only a minute portion of the gas while the chemical substrate treats the exhaust gas.
Birmingham et al., U.S. Pat. No. 4,954,320, discloses an alternating current discharge plasma device for decomposing toxic contaminants and removing hazardous aerosols in air. The device includes a nonconducting packing material disposed between two electrodes and a power supply to produce air plasma throughout the packing material.
In addition to the need for improved technology relating to reducing emissions from mobile and point sources, it is desirous to develop technology that generates a high concentration of ozone for a variety of other environmental purposes. For example, the introduction of ozone into cylinders of a vehicle's engine causes more complete combustion to occur. The superior combustion results in increased horsepower, improved mileage and a reduction in emissions.
Ozone is also effective in reducing bacterial and virus counts. As such, ozone can be used to treat effluent from municipal wastewater treatment plants. Currently, chlorine is typically mixed into an effluent to meet fecal chloroform and e-coli treatment standards. However, although chlorine dissipates quickly, an effluent containing chlorine is highly toxic to aquatic plants and animals. Chlorine is also deadly to humans, requiring extreme handling and storage safety measures to be taken.
Ozone may also be used for removing odors and smoke from an environment. For example, ozone closets may be used before dry cleaning in order to remove smoke from articles of clothing. As another example, ozone may be used to remove smoke, odors, air borne pathogens, or the like, from indoor air, such as a hotel room, factory or pub.
In practice, the beneficial uses of ozone have not been fully realized due to the inability of conventional ozone generating devices to cost effectively produce a sufficient quantity and concentration of ozone for the particular task. Other difficulties include that ozone breaks-down relatively quickly and that it is impractical to transport and store in quantity. As such, it is desirous to produce ozone at the point of intended use. Again, traditional ozone generating devices have not satisfied these needs.
In view of the forgoing, what is needed is for a device that reduces pollution from point source and mobile source exhaust streams. Additionally, there is a need for a device that enhances the performance and enlarges the effective life of a conventional catalytic converter as well as that of a catalytic converter having a reduced quantity of noble metals. There is also a need for a device that produces ozone in high concentrations for other environmental purposes such as improving combustion in a combustion engine, eliminating bacteria and purifying indoor air.